FANNY HELP

hi i need help about fans

i amstartin a grow in a..........basically a bin!
a plastic bin

but im going tochop two holes one at the top and one and the bottom
both for input and output fans, i will use plastic plumbing tubes. but i cant find a cheap method of ventilation im on a very tight budget of £25
so i was thinkin
ebuyer.com sells:
1 computer power supply= £10
3-4 fans - about £7

so will this do?
are computer fansok?
i really need a cheap solution
wat if i have four fans at the top (bin lid) makeit air tight and then have 3 holes at the bottom to act like a vacum effect???
please help

thanks